This invention relates to methods and means for analyzing the figure and surface roughness characteristics of grazing incidence optics, for example the type that would be utilized in the generation and propagation of directed energy in the X-ray and hard UV regions, and the type used in chemical lasers, excimer lasers, laboratory x-ray lasers, gamma ray lasers, and free electron lasers.
Optical components used in X-ray and hard UV radiation at grazing incidence are generally in the shape long narrow segments of cylinders. Other grazing incidence and beam coupling optics include a wide variety of aspheric surfaces such as off-axis paraboloids, toroids, ellipsoids, etc. Such aspheres are generally difficult to test by conventional interferometry since the diffraction limitation at visible wavelengths makes the interpretation of interferograms extremely difficult. Testing finished optics requires a noncontact arrangement to avoid potential accidents which could damage the surface.
In the past, such tests and measurements have been slow and created sensitivity to thermal and other environmental effects that have seriously impaired the effectiveness of instruments that attempted to measure the figure of optical surfaces to the tolerances necessary for grazing incidence X-ray, UV and imaging at other wavelengths by off-axis aspheric optics. Classical interferometers of the Twyman-Green or Fizeau types have shown sensitivity to vibration and turbulence, required complex null optics, and operated at slow speeds with limited accuracy.